The present invention relates to a process for manufacturing uranium dioxide powder from uranium hexafluoride using a wet process, which is suitable as a material for a firm pellet.
Manufacturing of uranium dioxide powder, a material for fuel of nuclear power reactor is carried out by ADU process as follows:
Namely, solid uranium hexafluoride (UF.sub.6) is heated to vaporize, the UF.sub.6 gas is hydrolyzed with deionized water to uranyl fluoride (UO.sub.2 F.sub.2) solution. The UO.sub.2 F.sub.2 solution is added with ammonium hydroxide to form ammonium diuranate (ADU) precipitate. This slurry is filtered, then there is obtained a cake. The cake is washed, dried and milled. The obtained ADU powder is supplied to a calcining and reducing kiln to manufacture uranium dioxide powder. The uranium dioxide powder manufactured by this process has generally a particle size of about 0.1-3 .mu.m and an example of the particle size distribution thereof is illustrated in FIG. 1.
Thus, an UO.sub.2 pellet, a fuel of nuclear power plant is manufactured from the uranium dioxide powder as a raw material.
Therefore, in that case, the pellet is required to have a high sinterability and a sufficient strength and not to be chipped and cracked in the surface. The sinterability and formability of these uranium dioxide powder depend largely on the properties thereof. Therefore, various investigations have been directed to improve the properties of UO.sub.2 powder. For example, in the official gazette of Patent Publication No. 12026/1967, it is disclosed that when coarse and inactive UO.sub.2 powder having a low sinterability and fine and active UO.sub.2 powder having a high sinterability are mixed in a definite ratio, the obtained mixed UO.sub.2 powder is minimum in densification during sintering and is suitable as a raw material for manufacturing a pellet having a sufficiently strength.
However, when UO.sub.2 powder is manufactured and regulated by the above mentioned process, it is required the coarse powder having a low sinterability and the fine powder having a high sinterability is separately manufactured and these two kinds of the powder are mixed uniformly, thereby making a process for manufacturing UO.sub.2 powder complicated. The present inventors have turned their attention to the invention disclosed above and have succeeded in accomplishing the present invention by dissolving the defects thereof.